Submersible pumping assemblies such as progressive cavity pumps and centrifugal pumps are suspended downhole in a wellbore by a string of production tubing. During pumping, fluid is discharged up the production tubing by the pump. When the pump stops, either intentionally or as a result of a failure of the pumping assembly, fluid in the production tubing string may flow back down into the pump causing the pump to reverse and potentially causing debris in the fluid to enter the pump. The debris remains in the pumping assembly and, when the pump is restarted, may cause damage to the pumping assembly.
Alternatively, in the case where an operator wishes to pull the pump and the production tubing from the wellbore, such as for servicing of the pumping assembly, the pump and production tubing may pack off resulting in fluid remaining in the production tubing. In order to reduce the weight of the loaded production tubing for extraction from the wellbore, a bailing operation may be required which is both costly and time consuming.
It is known to provide a valve above the discharge of an electrical submersible pump for draining the tubing above the pump when the pump shuts down. U.S. Pat. No. 6,289,990 to Baker Hughes Incorporated teaches a tubing shunt valve which is pressure actuated between a sealed position, wherein fluid communication between the production tubing and an annulus thereabout via shunt ports is prevented, and a drain position, wherein fluid is drained from the production tubing above the pump through shunt ports into the annulus. The Baker Hughes valve utilizes a single diameter valve cage having a seal interface which shifts across the shunt ports when moving between the sealed and drain positions. The Baker Hughes valve utilizes a spring biased valve head and shaft forming a piston which is confined within a bore in the valve cage. The valve head seals against a valve seat formed in the valve cage in the drain position. The valve seat is in fluid communication with the discharge of the pump therebelow. The shifting of the sleeve to the sealed or production position is reliant upon a friction resistance to shifting of the valve cage being less than a fluid force required to open the valve head when biased to the drain position. Applicant believes that any additional resistance due to fouling could prevent shifting of the valve cage to seal the shunt ports even though the pump may have overcome the biasing spring to cause the valve head to unseat and fluid to pass through the valve seat and the plurality of axial passages in the valve cage.
Further, the spring which biases the valve head must be matched to the depth of the well as a result of increasing hydrostatic pressure and therefore many iterations of the valve are required for use in wells of different depths.
There is a need for a drain valve which reliably seals the shunt ports through repeated movement of the valve between the sealed and drain positions and which is reliably and rapidly actuated between the sealed production position and the drain position when required.